Apparatus and method for expanding a stimulation lead body in situ

ABSTRACT

An implantable lead is provided with at least one extendable member to position therapy delivery elements, which may be electrodes or drug delivery ports, after the lead has been inserted into the body. The lead may formed as a resilient element which is contained in a retainer tube that may be removed to permit the lead to deploy. Alternatively, a non-resilient lead may be provided with a slotted retainer tube. A series of mechanical linkages for expanding and retracting the lead within the human body may be actuated with various mechanisms. A control system may be provided for closed-loop feedback control of the position of the extendable members. The invention also includes a method for expanding an implantable lead in situ.

BACKGROUND OF THE INVENTION

[0001] This invention relates to implantable leads for deliveringtherapy, in the form of electrical stimulation or drugs, to the humanbody. Specifically, this invention relates to implantable leads that maybe expanded, retracted or adjusted after implantation in the human body.This invention also relates to mechanisms for accomplishing suchexpansion, retraction or adjustment of such leads in situ. Further, thisinvention relates to control systems for controlling such expansion,retraction or adjustment of such an implanted lead.

[0002] Recent efforts in the medical field have focused on the deliveryof therapy in the form of electrical stimulation or drugs to preciselocations within the human body. Therapy originates from an implantedsource device, which may be an electrical pulse generator, in the caseof electrical therapy, or a drug pump, in the case of drug therapy.Therapy is applied through one or more implanted leads that communicatewith the source device and include one or more therapy delivery sitesfor delivering therapy to precise locations within the body. In drugtherapy systems, delivery sites take the form of one or more catheters.In electrical therapy systems, they take the form of one or moreelectrodes wired to the source device. In Spinal Cord Simulation (SCS)techniques, for example, electrical stimulation is provided to preciselocations near the human spinal cord through a lead that is usuallydeployed in the epidural space of the spinal cord. Such techniques haveproven effective in treating or managing disease and acute and chronicpain conditions.

[0003] Percutaneous leads are small diameter leads that may be insertedinto the human body, usually by passing through a Tuohy (non-coring)needle which includes a central lumen through which the lead is guided.Percutaneous leads are advantageous because they may he inserted intothe body with a minimum of trauma to surrounding tissue. On the otherhand, the types of lead structure, including the electrodes ordrug-delivery catheters, that may be incorporated into percutaneousleads is limited because the lead diameter or cross-section must besmall enough to permit the lead to pass through the Tuohy needle.

[0004] Recently, the use of “paddle” leads, like Model 3586 Resume® Leador Model 3982 SymMix® Lead of Medtronic, Inc., which offer improvedtherapy control over percutaneous leads, have become popular amongclinicians. Paddle leads include a generally two-dimensional set ofelectrodes on one side for providing electrical therapy to excitabletissue of the body. Through selective programmed polarity (i.e.,negative cathode, positive anode or off) of particular electrodes,electric current can be “steered” toward or away from particular tissuewithin the spinal cord or other body areas. Such techniques aredescribed by Holsheimer and Struijk, Stereotact Funct Neurosurg, vol.56, 199: pp 234-249; Holsheimer and Wesselink, Neurosurgery, vol. 41,1997: pp 654-660; and Holsheimer, Neurosurgery, vol. 40, 1997: pp990-999, the subject matter of which is incorporated herein byreference. This feature permits adjustment of the recruitment areasafter the lead has been positioned in the body and therefore provides alevel of adjustment for non-perfect lead placement. Such techniques aredisclosed in U.S. Pat. Nos. 5,643,330, 5,058,584 and 5,417,719, thesubject matter of which is incorporated herein by reference.Additionally, the value of a transverse tripole group of electrodes hasbeen demonstrated for spinal cord stimulation, as described by Struijkand Holsheimer, Med & Biol Engng & Comput, July, 1996: pp 273-276;Holsheimer. Neurosurgery, vol. 40, 1997: pp 990-999; Holsheimer et al.,Neurosurgery, vol. 20, 1998. This approach allows shielding of lateralnervous tissue with anodes, like the dorsal roots, and steering offields in the middle under a central cathode by use of two simultaneouselectrical pulses of different amplitudes.

[0005] One disadvantage recognized in known paddle leads is that theirinstallation, repositioning and removal necessitates laminectomies,which are major back surgeries involving removal of part of thevertebral bone. Laminectomies are required because paddle leads have arelatively large transverse extent compared to percutaneous leads. Thus,implantation, repositioning and removal require a rather large passagethrough the vertebral bone.

[0006] Another disadvantage with paddle leads is that optimalpositioning is often difficult during implant. For example, thetransverse tripole leads described above work optimally if the centralcathode is positioned coincident with the physiological midline of thespinal cord. Such placement is difficult since the doctor cannot see thespinal cord thru the dura during implant. Moreover, lead shifting mayoccur subsequent to implant, thereby affecting the to efficacy of thetherapy delivered from the lead.

[0007] Yet another disadvantage recognized with paddle leads is that thelead position may change merely with patient movement. For example, whena patient lies down, the spacing between an epidural lead and the spinalcord decreases to a large extent, so that it is often necessary to lowerthe amplitude of the stimulation by half. It is reasonable to assumethat steering effects of a tripole lead might also be affected if theCSF width changes dramatically, or if due to patient twisting oractivity, the orientation between the lead and spinal cord changes.

[0008] While the prior art has attempted to provide deformable leads,which may provide improved insertion characteristics or enhancedstability once inside the body, they have not succeeded in providing adevice which remedies the aforementioned problems. For example, U.S.Pat. No. 4,285,347 to Hess discloses an implantable electrode leadhaving a distal end portion with a laterally extending stabilizer,preferably in the form of curved loops. Similarly, and U.S. Pat. No.4,519,403 to Dickhudt discloses an inflatable lead for enhanced contactof the electrode with the dura of the spinal cord. U.S. Pat. No.5,121,754 to Mullett discloses a device to allow electrodes to move tomore lateral positions after insertion, when a stiffening guidewire usedduring insertion is removed. In Mullett's device, only one electrode canbe found at any particular longitudinal location, since only gentlecurves of the lead were designed, and the curves are not adjustableafter implant of the lead. Similar problems apply to the devicedisclosed by O'Neill in U.S. Pat. No. 4,154,247.

[0009] Patent Cooperation Treaty (PCT) Publication No. WO 93/04734 toGalley discloses a lead tip that has four spans that will bulge intofour different directions when a confining outer catheter is drawnproximally back over the lead body. The publication describes oneelectrode on the middle of each span. In situ in the epidural space,these four electrodes will form a to square or rectangularcross-sectional shape. Two of them might be pressed into the dura (atlateral positions) and the other two would be dorsal, against thevertebral bone. Only the electrodes nearest the spinal cord would beuseful for programming. While this could give two electrodes at the samelongitudinal position, their medial to lateral locations are difficultto control, and their ability to spread apart depends on the relativestresses in the spans and tissue-like adhesions that may be present.Other malecot-type lead tips have been proposed for positioning ofelectrodes in the heart (U.S. Pat. No. 4,699,147, Chilson and Smith,1985; U.S. Pat. No. 5,010,894, Edhag, 1989) or anchoring of lead bodies(U.S. Pat. No. 4,419,819, Dickhudt and Paulson, 1982; U.S. Pat. No.5,344,439, Otten, 1992) or positioning of ablation electrodes (Desai,U.S. Pat. No. 5,215,103, 5,397,339 and 5,365,926). While theaforementioned prior art devices provide various configurations forcompact insertion or lead stabilization after implant, they do not offerthe advantages and improved efficacy recognized with respect to paddlelead configurations.

[0010] It would therefore be desirable to provide a lead structure forstimulation of excitable tissue surfaces which combines the advantagesoffered by percutaneous leads with respect to minimized trauma duringinsertion, repositioning and removal with the advantages offered bypaddle-type leads with respect to improved efficacy, ability to provideelectrodes in places lateral to the axis of the lead and tailoring oftreatment.

[0011] It would also be desirable to provide a lead structure whichpermits adjustment of the lead dimensions and therefore the deliverysite location in situ for enhanced control of the therapy being appliedto the excitable body tissues.

[0012] It would be further desirable to provide a paddle lead which iscapable of automatically adjusting its width or delivery site spacingautomatically in response to patient factors such as body position oractivity or in response to a parameter such as muscle contraction oraction potentials, which may be characteristic of the stimulation ortherapy being applied.

SUMMARY OF THE INVENTION

[0013] The invention combines the advantages of percutaneous leads withthose of paddle leads. In a preferred embodiment, the invention providesa lead structure including a central core portion and at least oneflexible, semi-flexible or semi-rigid transversely extending span whichmay be positioned in a compact position during insertion in which it iswound around or otherwise disposed in close proximity to the centralcore portion. Each span may also be deployed or shifted to a position inwhich it extends outward from the central core portion in a transversedirection. Each span has disposed on one surface a number of therapydelivery elements, in the form of electrodes or catheter ports, fordelivering therapy in the respective form of electrical or drug therapyto the body. In the compact insertion position, the lead may be easilyinserted within a catheter or Tuohy needle. Once the lead has beenpositioned at the appropriate place in the body, the span or spans maybe deployed from the compact position to the extended position in whichthe therapy delivery elements are positioned in a fashion similar to apaddle lead. The flexibility of the spans also permits the lead to beretracted back to the compact position in the event that the lead mustbe removed from the body.

[0014] In a preferred embodiment, the invention provides a lead whichincludes a central core portion and at least one flexible paddleextending therefrom and which may be coiled around the core portion whenthe lead is to be compacted for insertion. As the lead is insertedthrough a catheter or Tuohy needle, the spans are kept in the compactposition by lead rotation in a direction opposite their direction ofwinding around the central core. Also according to the invention, thespans are deployed by rotating the central core portion in the samedirection in which the spans are coiled around the central core portion.Because of the flexibility of the spans, they are caused to moveoutward, away from the central core as the lead is uncoiled. In anotherembodiment of the invention, the spans can be formed of a resilientmaterial in which resilient forces develop when the lead is configuredin its compact position. The lead is maintained in its compacted formwhile inside of the insertion tool, i.e. Tuohy needle. The resilientforces cause the spans to extend outward once the lead exits the end ofthe insertion tool.

[0015] An outer concentric retainer tube may be provided in combinationwith the lead, the outer retainer tube acting to retain the lead in itscompact position during insertion. The retainer tube may be providedwith a pair of notches on its distal end to aid in the retraction of thelead after deployment. Specifically, the notches are disposed on thedistal end of the retainer tube in such a manner that the spans willengage the notches when the central core portion is rotated and pulledtoward a proximal end of the retainer tube. The notches retain the spansin position as the central core rotates, thus causing the spans to coilaround the central core portion and assume a compact position.

[0016] The present invention also provides a lead which may be compactedin a different manner than described above. The lead is comprised of aseries of therapy delivery elements which are attached to a thin backingsheet which permits the sheets to be disposed one on top of the other inthe compact insertion position and then to expand to a generally planarorientation once the lead is inserted to the appropriate position in thebody.

[0017] The following are exemplary advantages of adjustable leadsconstructed according to the preferred embodiments of the invention:

[0018] 1. The spacing of the sites can be matched to importantdimensions of the tissue affected, e.g., the width of the Cerebro-SpinalFluid (CSF) between the dura and the spinal cord.

[0019] 2. As the dimensions of the lead tip are changed, the locationsof the sites relative to the tissue affected may be advantageouslyaltered. For example, as a paddle's width is increased the paddle willmove toward the spinal cord in the semicircular dorsal part of theepidural space.

[0020] 3. In cases where the bones or fluid compartments have largewidths (e.g., CSF depth at spinal level T7 or T8) or are too wide in aparticular patient, the paddle width can be increased appropriately toensure effective therapy.

[0021] 4. Changes in paddle width and the accompanying medial andlateral movement of the sites can have a beneficial effect on thetherapy. For example, the ability to stimulate only the medial dorsalcolumns versus the more lateral dorsal roots may provide enhancedtherapeutic results.

[0022] 5. As the patient ages, their pathological condition changes,their degree of fibrosis or scar tissue changes, or the effects of thetherapy change, adjustments of the paddle dimension(s) might restore ormaintain the benefit.

[0023] 6. If the paddle's dimension(s) can be changed after implant, itmay be possible to optimize the benefits and minimize undesirable sideeffects.

[0024] 7. By changing the paddle's dimension(s), it may be possible toavoid surgery to replace or reposition the lead.

[0025] 8. By changing the paddle's dimension(s), it may be possible toposition the sites optimally relative to important physiologicallocations, e.g., the physiological midline of nervous tissue, orreceptors responsive to the drugs being delivered.

[0026] 9. It may be possible to minimize the use of energy by optimizingefficiency of therapy delivery through adjustment of paddle width.

[0027] 10. There may be minimal insertion trauma and operating room timeand resources needed if it is possible to place a lead with percutaneoustechniques, and then expand it in situ.

[0028] 11. Repositioning of a paddle lead can be done withoutlaminectomy. Removal is also made quicker and less traumatic.

[0029] 12. With closed loop feedback control of the paddle'sdimension(s), optimal therapy can be maintained with less interferencewith the patient's lifestyle.

[0030] Another preferred embodiment allows automatic changes in at leastone dimension of a paddle lead. Such a system would measure an effect ofthe stimulation, e.g., a compound action potential caused bystimulation/drugs, a muscle contraction, the direction of gravity,increased activity of the patient, relative motion of vertebral bones,or other effects. Measurement techniques for compound action potentialsare disclosed in U.S. Pat. No. 5,702,429 the subject matter of which isincorporated herein by reference. Such a recorded signal should bealtered if the lead paddle dimension that is controlled is changed.Then, after filtering, amplifying, integrating and comparing therecorded signal to a previous stored signal, the parts of the lead thatcontrol the dimension in question will be moved or activated, causing achange in said dimension, which will restore the effect measured to itsoriginal value. This constitutes closed loop feedback control, and canenable to patient to be less affected by changes in the therapy causedby his/her position, activity, etc. Of course there should be governorson the dimensional changes allowed, so that if the measured parameter isvery greatly changed, neither the device nor the patient will undergodamage or trauma. The described embodiments show preferred techniques toexpand a lead in directions transverse to the main axis of the leadbody. The invention also contemplates devices for expanding the lead ina direction substantially parallel to the lead axis.

[0031] Other advantages novel features, and the further scope ofapplicability of the present invention will be set forth in the detaileddescription to follow, taken in conjunction with the accompanyingdrawings, and in part will become apparent to those skilled in the artupon examination of the following, or may be learned by practice of theinvention. The advantages of the invention may be realized and attainedby means of the instrumentalities and combinations particularly pointedout in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings which are incorporated into and form apart of the specification, illustrate several embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating a preferred embodiment of the invention and are not to beconstrued as limiting the invention. In the drawings, in which likenumbers refer to like parts throughout:

[0033]FIG. 1 is a plan view of a lead according to the present inventionbeing inserted through a Tuohy needle near the dura of a human spine;

[0034] FIGS. 2A-2D are isometric views of a lead according to thepresent invention in a compact insertion position;

[0035]FIG. 2E is an isometric view of the lead of FIG. 2A in an expandedor deployed position;

[0036]FIG. 3 is an isometric view of a lead according to anotherembodiment of the invention;

[0037]FIG. 4A is an isometric view of a lead and retainer tube accordingto yet another embodiment of the invention;

[0038]FIG. 4B is an isometric view of a lead retainer tube according tothe present invention;

[0039]FIG. 4C is an isometric view of a lead and retainer tube accordingto the present invention;

[0040]FIG. 5A is an isometric view of a lead and expansion mechanismaccording to another embodiment of the present invention;

[0041]FIG. 5B is a top view of the lead of FIG. 5A in a compactposition;

[0042]FIG. 6A is a cross section of a lead according to anotherembodiment of the invention;

[0043]FIG. 6B is a front view of an expansion mechanism according to apreferred embodiment of the present invention;

[0044]FIG. 7 is a front view of an expansion mechanism according toanother preferred embodiment of the present invention;

[0045]FIGS. 8A and 8B are front views of an expandable lead according toanother preferred embodiment of the invention;

[0046]FIG. 8C is a front view of the expandable lead of FIGS. 8A and 8Bwith an alternative embodiment for the actuating mechanism;

[0047]FIGS. 9A and 9B are side and front views, respectively, of anotherpreferred embodiment of the present invention;

[0048]FIGS. 10A and 10B are front views of another preferred embodimentof the present invention;

[0049]FIGS. 11A and 11B depict yet another preferred embodiment of thepresent invention;

[0050]FIG. 12A is a front view of an adjustment mechansim according to apreferred embodiment of the invention;

[0051]FIG. 12B is a front view of an adjustment mechansism according toanother preferred embodiment of the invention;

[0052]FIG. 12C is a front view of an adjustment mechansim according toyet another preferred embodiment of the invention; and

[0053]FIG. 12D is a front view of an adjustment mechansim according tostill another preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054]FIG. 1 illustrates a lead according to a preferred embodiment ofthe invention being utilized in an SCS implementation. In accordancewith known techniques, a Tuohy needle 14 is positioned near the dura 12of spine 10. Lead body 20 is inserted through the lumen of Tuohy needle14 and positioned near the dura 12. A proximal end (not shown) of leadbody 20 is connected to a source device (not shown) which may be a pulsegenerator, in the case of electrical stimulation, or a drug pump in thecase of drug therapy. Although the invention will be described hereinwith reference to SCS procedures and the embodiments described inrelation to electrical therapy, it will be recognized that the inventionfinds utility in applications other than SCS procedures, including otherapplications such as Peripheral Nervous System (PNS) Stimulation, SacralRoot Stimulation, Cortical Surface Stimulation or Intravecular CerebralStimulation. In addition, the invention finds applicability to SCSprocedures where the lead is placed in the intrathecal (subdural) space.The invention also finds utility to drug therapy where electricalcomponents are replaced with conduits and catheters for conducting drugmaterial to the therapy site. In this case, especially, the lead may beplaced in the intrathecal space.

[0055]FIGS. 2A thru 2D illustrate a lead according to a preferredembodiment of the present invention. Lead 20 is provided with a distaltip 30 that may be compacted for insertion and unfolded after it hasbeen positioned appropriately within the body. Distal tip 30 includes acentral portion 32 which has at least one span 34 depending therefrom.Span 34 is comprised of a flexible, insulative material, such aspolyurethane or silicone rubber. The term “flexible” as used hereinrefers to both resilient and non-resilient materials. Central portion 32may have a generally semi-circular cross-section as shown, or may beflat. A central passage 33 may run axially along the inside of lead 20.A centering stylet 25 is provided through central passage 33 and extendsin a distal direction through central portion 32 for engaging a part ofthe body, such as adhesions in the epidural space, to stabilize lead tip30 as it is deployed. Affixed to a surface of spans 34 and to thecentral portion 32 is a series of other therapy delivery elements in theform of electrodes 36A-E. In accordance with the invention lead 20 maybe configured into a compact insertion position shown in FIG. 2A. Asshown in FIG. 2B, spans 34 are coiled around central portion 32 suchthat the lateral extent of lead tip 30 is no larger than the lumen ofTuohy needle 14.

[0056] Once in position within the epidural space, lead tip 30 may bedeployed out of the Tuohy needle 14, as shown in FIG. 2C. FIG. 2D showsthe view from the side opposite the side illustrated in FIG. 2C. In theembodiment described in which the spans are flaccid or semirigid,deployment of lead tip 30 may be implemented by rotating the lead body20 in a counterclockwise direction once lead tip 30 is beyond the end ofthe Tuohy needle in a desired position. As spans 34 encounter dura ordorsal bone of spinal canal, they can uncoil to assume a generallyplanar shape in which electrodes 36A-E are disposed on one side of thelead facing the dura, as shown in FIG. 2E. As shown in phantom in FIG.2D, electrodes 36A-E communicate electrically with the source device(not shown) via conductor paths 39 and 41. Conductor paths 39 and 41 maybe comprised of a flexible electrical conductor or thin wires which areembedded or molded within lead 20.

[0057] In the case of drug therapy, the electrodes 36A-E illustrated inFIGS. 2C-E would be replaced by ports which act as therapy deliveryelements to convey drug to the body. Similarly, conductor paths 39 and41 would be replaced by conduits formed in the interior of lead 20 forconveying drug from the source device. Stylet 25 may be left permanentlyin the epidural space or may be withdrawn from the lead 20 after thelead tip 30 is uncoiled. In the case of a drug delivery device, stylet25 might remain as a catheter at some preferred distance

[0058]FIG. 3 illustrates another embodiment of the invention in whichlead 20 is provided with a pair of guide pins 40 which are affixed to amore proximal removable sheath 41 that surrounds lead body 20.Alternatively, guide pins may be formed integrally on Tuohy needle (notshown). Guide pins 40 act to guide spans 34 outward as the lead body 20is rotated in a counterclockwise and to guide spans 34 to coil aroundcentral portion as lead body 20 is rotated in a clockwise direction.Guide pins 40 may be comprised of a rigid, material and may be extendedor retracted from sheath 41 or Tuohy needle 14. After spans 34 aredeployed, sheath 41 may be removed.

[0059]FIG. 4A illustrates another embodiment of the invention in whichspans 34 are formed as resilient or elastic elements. The term“resilient” as used herein refers a tendency to return to an undeformedstate once spans 34 are no longer compressed to lay beside central part32. In accordance with this embodiment of the invention, a retainer tube50 is provided to retain lead tip 30 in its compacted position untildeployment is desired. Retainer tube 50 includes an inner passage whichis sufficient to accommodate the diameter or lateral extent of lead body20 and its compact shape-changing tip 30. The outer diameter of retainertube 50 is small enough that retainer tube 50 may also be insertedthrough the lumen of Tuohy needle 14 (FIG. 1). Alternatively, tube 50may replace the Tuohy needle. Spans 34 are formed in such a manner thatthey have a tendency to undertake a position in which they are extendedfrom central portion 32. Thus, in the compact insertion positionillustrated in FIG. 4A, resilient forces are present in spans 34 to urgethem outward into their extended, uncoiled position. The resiliency ofspans 34 may derive from the polymeric material used to construct spans34 or from resilient elements like wires (not shown) which areincorporated into the interior or onto the exterior surface of spans 34.

[0060] Referring to FIGS. 4B and 4C, in accordance with yet anotherpreferred embodiment of the invention, a notch 60 is provided in adistal end 52 of retainer tube 50 to facilitate retraction of a deployedlead. Preferably, one notch is provided for each span 34 provided onlead tip 30. In operation, retainer tube 50 is inserted around aproximal end (not shown) of lead body 20 and pushed towards lead tip 30a sufficient distance until retainer tube 50 encounters lead tip 30.Lead body 20 is then pulled in a proximal direction and simultaneouslyrotated, in a direction which may be clockwise or counterclockwise,until lower edges 37 of spans 34 slide into notches 60. Under continuedrotation of lead tip 30 and lead 20, notches 60 function to guide spans34 into their coiled, compacted position. Once compacted, lead 20 may beretracted further into retainer tube 50. Compacted lead 20 and retainertube 50 may then be repositioned to a higher or lower point along thespinal cord or may be removed from the body.

[0061]FIGS. 5A and 5B illustrate an expandable lead tip 130 according toanother embodiment of the invention. Referring to FIG. 5B, lead tip 130is comprised of a series of electrodes 136A-E which are fastened to aflexible insulative backing sheet or span 140. The central portion oflead tip 130 is comprised of middle electrode 136C. Span 140 may beconstructed of polyurethane or DACRON-reinforced silicone rubber.Electrodes 136A-E are in electrical communication with source device(not shown) via a series of conductors 139 incorporated into or ontospan 140. Electrodes 136A-E are embedded in span 140 or fastened byadhesive or other known means. Ends 142 of span 140 are provided witheyelets 144 for fastening to an expanding mechanism which will bedescribed below. This aspect of the invention provides a lead tip 130which may assume a compacted position, in which electrodes 136A-E arestacked one on top of the other such that the thickness of lead tip 130may be reduced to a dimension that is slightly larger than thecollective thicknesses of electrodes 136A-E.

[0062] Referring to FIG. 5A, lead tip 130 may be expanded with the useof an expansion mechanism 150 according to one aspect of the invention.Expansion mechanism 150 comprises a series of struts 152 which arepivotally linked to one another such that points A and B may be causedto move towards and away from one another in order to compact or expandlead tip 130, respectively. A first linkage 156 is pivotally connectedto struts 152A and 152B. A second link 158 is pivotally connected tolinks 152C and 152D. First and second links 156 and 158 extend to aproximal end of lead body 10 where they can be individually actuated bya clinician. By moving first link 156 with respect to second link 158,points A and B are caused to move toward or away from one another,thereby contracting or expanding lead tip 130. By using rigid struts andlinkages, sufficient farces can be applied so that a space may becreated for the expanded size of lead tip 130. Introductory Sheath 170may be removed after lead tip 30 is expanded. Or, as another embodiment,it might remain in the position shown, and a locking mechanism to keeplinks 156 & 158 at a constant position might be able to compress sheath170 over the two links. A tether 180 sets a limit on the separation ofpoints A and B, and guarantees that electrodes are evenly spaced whenthe length of tether 180 equals the length of span 140.

[0063]FIGS. 6A and 6B illustrate another embodiment of the invention.FIG. 6A is a cross-section of a lead tip 230 according to a preferredembodiment of the invention which comprises a single span 234incorporating a series of conductors 236A-F therein. FIG. 6B illustratesa plan view of a mechanism 250 suitable for deploying lead tip 230 or astack of electrodes as shown in FIG. 5B. Mechanism 250 comprises a pairof links 252A and 252B pivotally connected to one another and eachpivotally connected to a respective actuator link 258A and 258B. Throughrelative movement of actuator links 258A and 258B, point A is caused tomove toward or away from link 258A, thereby causing contraction orexpansion of lead tip 230 or 130. One eyelet 144 on span 234 is attachedto point A, and the other eyelet may slide on link 258A. With thisembodiment, since the lead tip is pulled in one direction, mechanism 250in its initial, collapsed position, should be positioned toward oneside, for example, over the dorsal roots on one side of the spinal cord.In the expanded position, point A would advance to the opposite dorsalroots. Once again, a way to lock point A at a certain expanded positionis to have an anchor along sheath 170 that compresses and holds sheath170 against links 258A and 258B. Like mechanism 150, by using rigidstruts and linkages, a space can be created for lead tip 230.

[0064]FIG. 7 illustrates an expansion mechanism according to anotherpreferred embodiment of the invention. Lead tip 130 may be expanded withthe use of mechanism 350, comprised of struts 311 and 310. Linkage 330is pivotally connected to the end of these struts. Linkage 340 ispivotally connected to the center of these struts. As linkages 330 and340 are moved relative to each other be a clinician, tips 360 will movetogether or apart. Eyelets 144 of lead tip 130 (FIG. 5B) can beconnected to tips 360.

[0065]FIGS. 8A and 8B illustrate an expandable lead according to anotherpreferred embodiment of the present invention. The lead comprises aflexible outer coaxial accessory tube 802 which is mounted over thedistal end of lead body 801. A stop 806 is affixed to the distal end oflead body 801 to prevent movement of the upper end 830 of accessory tube802 relative to lead body 801. The lower end 832 of accessory tube 802is adapted to slide with respect to lead body 801. Accessory tube 802includes a central slot 805 forming two flexible leaf portions 820 and822. A recess 824 is provided in each leaf portion 820 to form a bendingjoint therein. The lower end 832 may be moved upward, thereby causingleaf portions 820 to bend and deploy outward from the lead body 801. Toaccuate the mechanism an actuator 807 is slid over the axial tube 801 bythe clinician. While holding onto the axial tube 801, the clinicianpushes the actuator 807 against the accessory tube which causes the slot805 to separate and the lead to open as illustrated in FIG. 8B. A seriesof ratchet rings 811, 812 and 813 are formed in lead body 801 to preventdownward movement of lower end 832 of accessory tube 802 to therebyretain the leaf portions 820 in their outward, deployed position. Theserachet rings will also allow and hold different amounts of lateralexpansion to be chosen by the clinician. A rigid barrel electrode 803 ismounted on each leaf portion 820 of the accessory tube 802. In theexpanded position of accessory tube 802, central electrodes 808. 809 and810 are exposed. Central electrodes 808, 809 and 810 and barrelelectrodes 803 communicate electrically with the source device (notshown) through electrical conductors (not shown) within the lead body.

[0066]FIG. 8C illustrates an expandable lead according to anotherpreferred embodiment of the present invention. This embodiment is thesame as that illustrated in FIGS. 8A and 8B except that a screw actuatoris provided for precise adjustment of the outward deployment of leafportions 820. The axial lead body 801 has a threaded portion 811 formedtherein. A threaded drive nut 812 is mounted on the threaded portion ofthe lead body 811. The drive nut has multiple indented holes 812 a toreceive an actuation driver similar to 813. The drive nut is interlockedby pins (813 a) on an actuation driver 813 and rotated by the driver.This screw apparatus allows finer adjustment of the expansion and alsoadjustment of the expansion after implantation of the lead device.

[0067]FIGS. 9A and 9B illustrate another embodiment of the invention.Mechanism 450 can have a central element 410 that may contain anelectrode or catheter port 405. It may house progressively smallermobile telescoping parts 420, 430, 440 that can be pushed outward towardone or more directions. Each mobile part is provided with a shoulder 422to limit its outward movement and to recruit an adjacent mobile part. Atab 424 is provided to limit inward movement. For an expansion in oneplane, element 410 may have inside it one or more mechanisms 150 (FIG.5A), 250 (FIG. 6B) or 350 (FIG. 7). Alternatively. there might besingle, curved linkage passing along lead 20 and attached to the finalelectrode or catheter port site 445. As this linkage is moved by aclinician, site 445 will move outward or inward, and itermediate siteswill follow if the movement of each site relative to the next site islimited.

[0068]FIGS. 10A and 10B illustrate another embodiment of the invention.In FIG. 10A, the lead 20 is in a compacted position, with elastic andresilient transverse spans 500 bent to remain inside the lumen of Tuohyneedle 14. Spans 500 are adapted to bend to a position substantiallyparallel to the axis of lead 20 in the compact position. Once the leadis pushed beyond the needle, spans 500 will move by their resiliency totheir natural position, as shown in FIG. 10B. Those of ordinary skillwill note that the grouping of central electrode or catheter port 510and the two nearest side electrodes or ports 520 form a tripole/triportarrangement transverse to the longitudinal direction of the lead 20. Theclinician may have to place and manipulate a mechanism like 150, 250 or350 prior to placement of this lead to create a space. Alternatively, ametal material like NITINOL may be placed inside span 500 and treated sothat its position after removal of the confinement of needle 14 will beperpendicular to the lead axis.

[0069]FIGS. 11A and 11B illustrate another embodiment of the invention.In FIG. 11A, the lead 20 is in a compacted position with elastic andresilient spans 600 bent to remain inside the lumen of Tuohy needle 14.There is a central electrode or catheter port 610. The lateralelectrodes/ports 620 are on members that will remain parallel to thelead axis due to pivot points 630 and equal length spans 600 above andbelow.

[0070] In FIG. 11B, the lead tip is beyond the introducing needle. Thespans 600 resume their normal, unstressed positions perpendicular to thelead body axis. Lateral electrodes/ports 620 are on either side ofcentral electrode/port 610. Removal may be accomplished by pulling onthe lead body with sufficient force to bend the spans 600 back along thelead body, or by pushing another catheter or needle over lead 20. It isrecommended that there be a thin, inert and flexible film (not shown)over the space between spans to help removal by preventing tissueingrowth. One embodiment of the invention is to lock linkages as shownin FIGS. 5-7 into a fixed orientation by using a compressive sleeve tosqueeze the lead body 20 inward against the linkages. This sleeve may bean anchor to superficial (subcutaneous) tissue. To make a change, minorsurgery can be done to cut down to this anchor, loosen or remove it,adjust the positions of the linkages, replace the anchor/compressivesleeve, and resuture the wound. Obviously, the clinician and patientneed to believe that the benefits of such a procedure out weigh thediscomfort and risks.

[0071]FIGS. 12A through 12D illustrate mechanisms that may be used tooperate the linkages illustrated and described with respect to FIGS. 5A,6B, 7 and 9 in accordance with preferred embodiments of the invention.FIG. 12A illustrates an embodiment of the invention that allows chronicadjustment of the relative positions of two actuating members 710 and720. A rigid needle 775 with a sharp hexagonal tip 785 is passed throughthe skin and engages a hexagonal receptacle (possibly via reductiongears) 790 that is capable of turning a circular component 760 inside ofa container 750 beneath the patient skin. On end of this container 750attaches to the lead body 20, which contains the two actuating members710 and 720 and wires/catheters 730 that go to the distal tip of thelead 20. Another end of the container 750 connects to a lead 721 thatconveys the wires/catheters 730 to a source device (not shown).Actuating members 710 and 720 are connected to the rotating component760 are connected to the rotating component 760 by pivot points 770 and780. As the needle 775 is rotated, the linkages 710 and 720 will moverelative to each other. This device 750 should be large enough to bepalpated under the skin, and the rotating component 760 should be largeenough so that limited rotation of approximately 60° causes sufficientmovement of the linkages.

[0072]FIG. 12B illustrates another preferred embodiment of a linkageactuating mechanism according to a preferred embodiment of theinvention. This embodiment allows chronic adjustment of the position ofone linkage 810 relative to the lead body 20 using a rack gear andpinion gear arrangement. This embodiment may be used with atwo-actuating member configuration as described with respect to FIG.12A, where one actuating member is fixed with respect to lead body 20.As in the embodiment described above with respect to FIG. 12A, a rigidneedle (not shown) with a hex-head sharp tip is passed through thepatient's skin and engages a hexagonal receptacle 865 that drives aninternal gear 860 of subcutaneous container 850. As gear 860 turnspossibly with the aid of reducing gears, it will move the actuatingmember 810 back or forth, which has gear teeth 840 formed on itsproximal end. A stop 870 prevents excessive movement of actuating member810. A wire/catheter group 830 passes from lead 20 through the containerto another lead 821 from the source device. Alternatively, the sourcedevice could be on the back side of the container 850. It will berecognized by those of ordinary skill that there could be a number ofgears inside container 850 to change the direction of movement of theactuating member 810, for example, to a rotary direction.

[0073]FIG. 12C illustrates another preferred embodiment of a linkageactuating mechanism according to a preferred embodiment of theinvention. This embodiment allows chronic adjustment of the position oflinkage 910 relative to the lead body 20. Again, this embodiment may beused with two linkage configurations where on linkage is fixed withrespect to the lead body 20. This embodiment utilizes a hydrauliccylinder arrangement to actuate linkage 910. In this case a noncoringhypodermic syringe needle (not shown) is passed through the patient'sskin and through a compressed rubber septum 960 provided on the side ofcontainer 950. Fluid may be added or withdrawn from beneath the septum,which is connected to a syringe 940. The moveable plug of this syringe920 is connected to the moveable linkage 910. Again, the wires/catheters930 from the proximal tip of lead 20 pass through container 950 and onto the source device. Alternatively, the source device could be on theback side of container 950, although, for drug delivery, there wouldneed to be another system on the front of container 950 for refillingthe drug.

[0074]FIG. 12D illustrates an actuating mechansim according to apreferred embodiment of the present invention that allows chronicadjustment of the degree of rotation of linkage 1010 relative to leadbody 20. A rigid needle with a hex-head sharp tip can be inserted into ahexagonal receptacle 1070 in container 1050. Rotation of this needledevice rotates gear 1020 which causes rotation of gear 1040 attached tolinkage 1010. There may be restrictions on the movement of gear 1020 toprevent excessive rotation.

[0075] The embodiments shown in FIGS. 12A-D demonstrate devices toactuate linkages that pass to the distal tip of the lead and causechanges in one or more dimensions of the lead paddle. As described,these involve transmission of force or energy through the skin by meansof a needle that passes through the skin. The same effects can beachieved by having a small motor implanted into the container partsshown, or into the power source itself (not shown) which runs on anelectrical battery or transmitted and received radio frequency signal,such as the motor provided in the totally implantable, programmable drugdevice called SynchroMed®, manufactured by Medtronic, Inc. ofMinneapolis, Minn. Smaller motors may be acceptable, especially if asequence of gears may be used to provide mechanical advantage. If suchmotors are used, there should be a mechanical circuit breaker to preventexcess motion of the linkages.

[0076] Very similar techniques would allow expansion of a lead in adirection parallel to the lead body. For example, telescoping elementswith electrodes could move parallel to the axis of the lead body(parallel to the spinal cord), similar to the way a car antenna can beextended and retracted. By attaching electrodes and catheter ports tothe axial linkages of FIGS. 5 through 8, or attaching eyelets 144 ofcompacted groups of electrodes/ports such as items 130 or 230, it ispossible to extend or compact said groups of electrodes in an axialdirection. This is a valuable feature if one wishes to match the axialspacing of electrodes/ports to important dimensions of the structure tobe stimulated/affected. For example, Holsheimer (Neurosurgery, vol. 40,1997: pp 990-999) has shown that there may be preferred longitudinalspacing of electrodes based upon the recruitment factors in spinal cordtissue, and also critically dependent upon the width of the CSF(cerebrospinal fluid) layer between the spinal cord dorsal surface andthe dura mater. Therefore, we wish to include the ability to increase ordecrease the longitudinal spacing between electrodes/ports by theseinventions, and to be able to make a change in said spacing afterinitial implant of a complete therapeutic system.

[0077] Those skilled in the art will recognize that the preferredembodiments may be altered or amended without departing from the truespirit and scope of the invention, as defined in the accompanyingclaims.

What is claimed is:
 1. An implantable lead for providing therapy to abody comprising: an elongate central portion; and at least oneextendable member having an end, the extendable member depending fromthe central portion and being adapted to assume a compact position, inwhich the end is disposed in close proximity to the central portion, andan extended position, in which the end is disposed at a location distalfrom the central portion; at least one therapy delivery element disposedon the extendable member for delivering therapy to the body.
 2. Theimplantable lead according to claim 1 , wherein the extendable member isa span adapted to coil around the central portion when the span is inthe compact position.
 3. The implantable lead according to claim 2 ,wherein the span incorporates a resilient material to urge the spantowards the extended position.
 4. The implantable lead according toclaim 3 , further comprising therapy delivery elements disposed on thespan for delivering therapy to the body.
 5. The implantable leadaccording to claim 2 , further comprising a central passage in thecentral portion for accommodating a centering stylet to stabilize andcenter the lead.
 6. The implantable lead according to claim 2 , furthercomprising a retainer tube having a notch for guiding the span to itsextended position.
 7. The implantable lead according to claim 2 ,wherein the span is adapted to be folded in such a manner that thetherapy delivery elements are disposed one on top of the other in thecompact position.
 8. The implantable lead according to claim 1 , whereinthe extendable member is formed as a coaxial accessory tube mounted overa distal end of the central portion, the accessory tube including acentral slot forming at least two flexible leaf portions.
 9. Theimplantable lead according to claim 8 , wherein a lower end of theaccessory tube is adapted to slide with respect to the central portion,the flexible leaf portions adapted to extend outward as the lower endslides.
 10. The implantable lead according to claim 1 , wherein theextendable member is formed as a series of telescoping elements.
 11. Theimplantable lead according to claim 10 , wherein the telescopingelements are provided with therapy delivery elements thereon.
 12. Theimplantable lead according to claim 1 , wherein the extendable member isformed as a resilient transverse span adapted to bend to a compactposition in which the extendable member extends in a directionsubstantially parallel to an axis of the lead and wherein the extendablemember is adapted to extend in an extended position at an angle of 90degrees or less to the axis of the lead.
 13. The implantable leadaccording to claim 1 , further comprising a linkage assembly forexpanding the lead.
 14. The implantable lead according to claim 13 ,wherein the linkage assembly comprises a first and second actuatingmembers adapted to move in a direction substantially parallel to an axisof the lead.
 15. The implantable lead according to claim 14 , furthercomprising a mechanism for adjusting the relative positions of the firstand second actuating members.
 16. The implantable lead according toclaim 15 , wherein the mechanism comprises a rotatable circularcomponent cooperatively associated with the first and second actuatingmembers.
 17. The implantable lead according to claim 15 , wherein themechanism comprises a rack gear and pinion gear, the rack gear beingcooperatively associated with one of the first and second actuatingmembers.
 18. The implantable lead according to claim 15 , wherein themechanism comprises a hydraulic cylinder adapted to adjust the relativepositions of the first and second actuating members.
 19. The implantablelead according to claim 13 , wherein the linkage assembly comprises arotatable shaft.
 20. The implantable lead according to claim 19 ,further comprising a gear mechanism for imparting rotational movement tothe shaft.
 21. An implantable lead for providing therapy to a bodycomprising: an elongate central portion; and at least one extendablemember having an end, the extendable member depending from the centralportion and being adapted to assume a compact position, in which the endis disposed in close proximity to the central portion, and an extendedposition, in which the end is disposed at a location distal from thecentral portion; at least one therapy delivery element disposed on theextendable member for delivering therapy to the body; and a linkageassembly for permitting adjustment of the position of the extendablemember in situ.
 22. The implantable lead according to claim 21 , whereinthe extendable member is a span adapted to coil around the centralportion when the span is in the compact position.
 23. The implantablelead according to claim 22 , wherein the span is adapted to be folded insuch a manner that the therapy delivery elements are disposed one on topof the other in the compact position.
 24. The implantable lead accordingto claim 21 , wherein the extendable member is formed as a coaxialaccessory tube mounted over a distal end of the central portion, theaccessory tube including a central slot forming at least two flexibleleaf portions.
 25. The implantable lead according to claim 24 , whereina lower end of the accessory tube is adapted to slide with respect tothe central portion, the flexible leaf portions adapted to extendoutward as the lower end slides.
 26. The implantable lead according toclaim 25 , further comprising a screw mechanism for adjusting theposition of the lower end of the accessory tube.
 27. The implantablelead according to claim 21 , wherein the extendable member is formed asa series of telescoping elements.
 28. The implantable lead according toclaim 21 , wherein the linkage assembly comprises a first and secondactuating members adapted to move in a direction substantially parallelto an axis of the lead.
 29. The implantable lead according to claim 28 ,further comprising a mechanism for adjusting the relative positions ofthe first and second actuating members.
 30. The implantable leadaccording to claim 29 , wherein the mechanism comprises a rotatablecircular component cooperatively associated with the first and secondactuating members.
 31. The implantable lead according to claim 29 ,wherein the mechanism comprises a rack gear and pinion gear, the rackgear being cooperatively associated with one of the first and secondactuating members.
 32. The implantable lead according to claim 29 ,wherein the mechanism comprises a hydraulic cylinder adapted to adjustthe relative positions of the first and second actuating members. 33.The implantable lead according to claim 21 , wherein the linkageassembly comprises a rotatable shaft.
 34. The implantable lead accordingto claim 33 , further comprising a gear mechanism for impartingrotational movement to the shaft.
 35. An implantable lead system forproviding therapy to a body comprising: an elongate central portion; atleast one extendable member having an end, the extendable memberdepending from the central portion and being adapted to assume a compactposition, in which the end is disposed in close proximity to the centralportion, and an extended position, in which the end is disposed at alocation distal from the central portion; at least one therapy deliveryelement disposed on the extendable member for delivering therapy to thebody; an actuating assembly for permitting adjustment of the position ofthe extendable member in situ; a sensor for sensing a stimulationparameter; a closed-loop feedback controller for operating the actuatingassembly to maintain the stimulation parameter at a predetermined value.36. A method for expanding an implantable lead in situ in the body, thelead including an expandable member having therapy delivery elementsthereon, the method comprising the steps of: inserting the lead into thebody; expanding the lead while the lead is in the body to thereby expandthe expandable member such that the relative positions of the therapydelivery elements may be adjusted.